The present invention relates to a work comfort evaluating device and method for evaluating a level of comfort of work by measuring myoelectric potentials of plural deltoid muscles when the work is done by antagonistic activities of the deltoid muscles. More particularly, the invention relates to a device and method for evaluating a steering comfort of a vehicle.
At present, automobile manufacturers and tire manufacturers pursue steering easiness of a vehicle and develop vehicles and tires by using various methods in order to provide such vehicles as automobiles, and tires, which ensure comfortable steering operations. In the development of the vehicles and tires, a steering comfort is evaluated, in most cases, by using a subjective sensory evaluation of a driver, or by using a method in which physical measurement data representing a behavior of the vehicle is acquired by using a measuring sensor such as an acceleration sensor that is attached to the vehicle, and the vehicle behavior is quantitatively measured.
To evaluate a level of work load imparted when given work is done, an electromyogram depicting signal waveforms of myoelectric potentials of a worker is used, and loads imparted to the muscles of the worker are quantitatively grasped. Since the measurement itself of the myoelectric potential is simple and good in its adaptation, it is thought that a level of the work load imparted when given work is done can properly be evaluated when the electromyogram is used. Further, there is a possibility that the evaluating method using the electromyogram is applied to the steering operation of the vehicle by the driver.
JP 2002-225585 A discloses a technique in which a myoelectric potential of a muscle acting to extend the arm and a myoelectric potential of another muscle acting to contract the arm are both measured, a value (conflict value) concerning a conflict of those two myoelectric potentials is calculated, and a level of driving load on the driver is determined based on the conflict value. More specifically, myoelectric potentials of the muscles of the driver which conflictingly act are measured by using myoelectric potential sensors, and a conflict feature quantity is calculated from a conflict value of the myoelectric potentials measured. When the calculated conflict feature quantity exceeds a predetermined threshold value, it is judged that the driving load on the driver has increased (paragraphs [0031] to [0038] in JP 2002-225585 A).
To obtain the threshold value used for the judgment, as shown in FIG. 10 in JP 2002-225585 A, the myoelectric potentials are measured for a long time, for example, 10 minutes, 8 minutes or 5 minutes, and a conflict value is calculated based on the measurement results. A conflict feature quantity for calibration, such as maximum values and average values, is calculated from the conflict value obtained by the long-time measurement. The threshold value in question is determined by multiplying the calculated feature quantity by a preset coefficient. Thus, to determine the threshold value, the long time measurement of 10 minutes, for example, is required. During this measurement time, the driving load on the driver cannot be judged. To cope with this, in JP 2002-225585 A, the data of the previous driving by the driver is used as a reference (paragraph [0040] in JP 2002-225585 A).
It is known that the myoelectric potential level frequently takes a different value when the myoelectric potential is measured because every time the sensors are stuck onto parts of the muscles before the measurement. If the data of the previous driving is used, which contains the myoelectric potential level that is probably different from the level of the current measurement, the judgment of the driving load on the driver will be erroneous. That is, the conflict feature quantity for calibration, which is used for determining the threshold value, is calculated from the myoelectric potential which will take a different value every time the detecting sensors are stuck. As a result, the conflict feature quantity for calibration also takes a different value every time the sensors are stuck. Accordingly, if the threshold value is determined by multiplying the conflict feature quantity for calibration by a fixed coefficient, judgment of the driving load on the driver will be erroneous.
The driving load on the driver disclosed in JP 2002-225585 A is a combination of a mental burden as to whether the driving is easy for the driver and a physical load when the driver actually drives. Accordingly, in a case where a large steering force is required for operating the steering wheel depending on the type of tires mounted, the physical load imparted to the steering wheel is large and the driving load increases. In this case, the steering force is large and a stable steering is secured, giving the driver a sense of safety and making the mental load less. However, the increase of the steering force results in an increase of the driving load.
In JP 2002-225585 A, the driving load on the driver is evaluated by using threshold values preset for respective running modes of high-speed cruising, highway congestion and city-area driving. Therefore, it is impossible to know a difference of the driving load caused by the mental burden on the drive in the high-speed cruising mode from the mental load in the highway congestion mode.
Such problems also occur not only in the evaluation of the steering operation of the vehicle but also in a case where a comfort is evaluated at work where an object to be operated is operated by antagonistically activating plural muscles (a pair of muscles, for example) of a human body.